如何在MongoDB聚合框架中处理零除 [英] How to handle division by zero in MongoDB aggregation framework

问题描述

我收集了可以上调或下调的项目.

I have a collection of items that can be upvoted or downvoted.

{"_id" : 1, "name": "foo", "upvotes" : 30, "downvotes" : 10}
{"_id" : 2, "name": "bar", "upvotes" : 20, "downvotes" : 0}
{"_id" : 3, "name": "baz", "upvotes" : 0,  "downvotes" : 0}

我想用聚合来计算质量

db.items.aggregate([
    {"$project":
        {
            "name": "$name",
            "upvotes": "$upvotes"
            "downvotes": "$downvotes",
            "quality": {"$divide":["$upvotes", "$downvotes"]}
        }
    },
    {"$sort": {"quality":-1}}
]);

显然这是行不通的，因为被零除.我需要实施适当的条件:

Obviously this doesn't work, because of division by zero. I need to implement appropriate conditioning:

如果赞成！= 0且反对== 0，则质量=赞成 如果upvotes和downvotes均为0，则质量为0

if upvotes != 0 and downvotes == 0 then the quality = upvotes if upvotes and downvotes are both 0 then the quality is 0

我尝试使用三元成语将数字减1.但是无济于事.

I tried tweaking downvotes by 1 using ternary idiom. But to no avail.

db.items.aggregate([
    {"$project":
        {
            "name": "$name",
            "upvotes": "$upvotes",
            "downvotes": "$downvotes" ? "$downvotes": 1
        }
    },
    {"$project":
        {
            "name": "$name",
            "upvotes": "$upvotes"
            "downvotes": "$downvotes",
            "quality": {"$divide":["$upvotes", "$downvotes"]}
        }
    },
    {"$sort": {"quality":-1}}
]);

如何在mongodb聚合框架中集成这种条件?

How can I integrate this kind of conditioning within mongodb aggregation framework?

推荐答案

您可能想使用 $ cond 运算符来处理此问题:

You might want to use the $cond operator to handle this:

db.items.aggregate([
    {"$project":
        {
            "name": "$name",
            "upvotes": "$upvotes",
            "downvotes": "$downvotes",
            "quality": { $cond: [ { $eq: [ "$downvotes", 0 ] }, "N/A", {"$divide":["$upvotes", "$downvotes"]} ] }
        }
    },
    {"$sort": {"quality":-1}}
]);

这篇关于如何在MongoDB聚合框架中处理零除的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！